An injection-molding die comprises a stationary die plate and a movable die plate for providing a cavity when closed, into which a molten resin is injected, and the parting of the movable die plate from the stationary die plate makes it possible to remove an injection-molded product having a shape corresponding to the cavity from the die. If the injection-molded product had undercut, the die would have a complicated structure to enable the removal of the injection-molded product. Accordingly, the injection-molded product preferably has a shape with as little undercut as possible.
For instance, some of injection-molded synthetic resin front bumpers for automobiles have openings in their bodies, to which grilles as separate members are fixed, but many of them have undercut in grille-fixing portions such as screw seats, etc. (see JP 2002-59794 A).
If there were no undercut in the grille-fixing portions of the front bumpers, the grille-fixing portions would likely be exposed from the edges of the openings of the front bumper bodies. Accordingly, the grille-fixing portions would be seen from front, providing poor appearance, and the grilles would have reduced opening area, leading to the reduction of an air flow to radiators.
JP 2000-108821 A discloses, as a mechanism of fixing a grille to a front bumper, a mechanism comprising projections extending rearward from an opening edge of the front bumper, through-holes formed in a flange of the grille for receiving the projections, and stoppers engageable with the projections penetrating the through-holes. The above mechanism further comprises a means for fixing the flange to the opening edge of the front bumper, and a mechanism for fixing the flange of the grille to the opening edge of the front bumper by screws. In the grille-fixing mechanism of JP 2000-108821 A, the grille-fixing portion is not exposed from the opening edge of the front bumper body, and the front bumper body is free from undercut.
However, the above fixing mechanism of JP 2000-108821 A needs the stoppers of the projections, and the flange-fixing means serve only to reduce the number of fasteners such as screws, etc., failing to fix the grille by themselves. In addition, the flange-screwing mechanism needs screws. Thus, the grille-fixing mechanism of JP 2000-108821 A needs a large number of fasteners, resulting in poor operation efficiency.